California Trail - Sweetwater River - Crossing The Sierra Nevada

Crossing The Sierra Nevada

The high, rugged Carson Range and Sierra Nevada mountains on the eastern California border were the final obstacles that had to be overcome before westbound travelers could proceed. The Sierras comprise a large block of weather-worn granite tilted towards the west. They extend about 400 miles (640 km) from near the Fandango Pass in the north to the Tehachapi Pass in the south. The western slopes are scarred by glacier and river carved canyons but slope much more gradually west taking about 70 miles (110 km) to fall from their rugged over 7,000 feet (2,100 m) crests to the about 25 feet (7.6 m) elevation of the Central Valley. The even more rugged glacier and river scarred eastern slopes are typically much more precipitous, rising to the rugged Sierra crest from their about 4,000 feet (1,200 m) base in the Great Basin in many places in less than 10 miles (16 km).

Precipitation in the Sierras flows to the Pacific Ocean if it falls on the western slope of the Sierras. If precipitation falls on the eastern side of the Sierra crest it flows into the Great Basin where it evaporates, sinks underground or flows into lakes and/or sinks (mostly saline). These sinks are often dry alkali laden flats late in the year. The eastern side lies in a rain shadow getting much less rain than the western side. Creeks, streams, or rivers originating east of the Sierra crest find no outlet to either the Gulf of Mexico or the Pacific Ocean. (The water piped over and through the Sierras to Los Angeles is the only exception.)

A second smaller but yet significant block of weather worn granite formed the Carson Range of mountains located east of today's Lake Tahoe, between the two ranges. From the Humboldt River Route, first the Carson Range and then the Sierras would have to be passed to get to western California. Even today there are only about nine roads that go over the Sierras and about half of these may be closed in winter. See: National Park Service California Trail Map